diff --git a/desktop/src/features/channels/ui/ChannelPane.tsx b/desktop/src/features/channels/ui/ChannelPane.tsx
index e66600e407..3984d20dcf 100644
--- a/desktop/src/features/channels/ui/ChannelPane.tsx
+++ b/desktop/src/features/channels/ui/ChannelPane.tsx
@@ -132,7 +132,7 @@ export const ChannelPane = React.memo(function ChannelPane({
   onThreadScrollTargetResolved,
   onThreadPanelResizeStart,
   onTargetReached,
-  onTimelineAtBottomChange,
+  onTimelineReadPresenceChange,
   onToggleReaction,
   onUnfollowThread,
   unfollowThreadById,
@@ -629,7 +629,7 @@ export const ChannelPane = React.memo(function ChannelPane({
               onSendVideoReviewComment={
                 activeChannel?.archivedAt ? undefined : onSendVideoReviewComment
               }
-              onAtBottomChange={onTimelineAtBottomChange}
+              onReadPresenceChange={onTimelineReadPresenceChange}
               onTargetReached={onTargetReached}
               onToggleReaction={onToggleReaction}
               targetMessageId={targetMessageId}
diff --git a/desktop/src/features/channels/ui/ChannelPane.types.ts b/desktop/src/features/channels/ui/ChannelPane.types.ts
index acb770df63..cfb25ec710 100644
--- a/desktop/src/features/channels/ui/ChannelPane.types.ts
+++ b/desktop/src/features/channels/ui/ChannelPane.types.ts
@@ -139,7 +139,10 @@ export type ChannelPaneProps = {
     } | null,
   ) => Promise<void>;
   onTargetReached?: (messageId: string) => void;
-  onTimelineAtBottomChange?: (atBottom: boolean) => void;
+  onTimelineReadPresenceChange?: (presence: {
+    isAtBottom: boolean;
+    readAt: number | null;
+  }) => void;
   onToggleReaction?: (
     message: TimelineMessage,
     emoji: string,
diff --git a/desktop/src/features/channels/ui/ChannelScreen.tsx b/desktop/src/features/channels/ui/ChannelScreen.tsx
index 5d5db71be4..0639540bfb 100644
--- a/desktop/src/features/channels/ui/ChannelScreen.tsx
+++ b/desktop/src/features/channels/ui/ChannelScreen.tsx
@@ -44,7 +44,6 @@ import {
 import { buildMessageComposerEditTarget } from "@/features/messages/lib/draftMentionRefs";
 import { formatTimelineMessages } from "@/features/messages/lib/formatTimelineMessages";
 import { DeleteMessageConfirmDialog } from "@/features/messages/ui/DeleteMessageConfirmDialog";
-import { getThreadReference } from "@/features/messages/lib/threading";
 import {
   resolveTimelineLoadingLatch,
   selectTimelineLoadingState,
@@ -78,6 +77,7 @@ import { useChannelAgentSessions } from "./useChannelAgentSessions";
 import { useMessageProfiles } from "./useMessageProfiles";
 import { useChannelPanelHistoryState } from "./useChannelPanelHistoryState";
 import { useScopedAtBottom } from "./useScopedAtBottom";
+import { useScopedTimelineReadPresence } from "./useScopedTimelineReadPresence";
 import { useChannelProfilePanel } from "./useChannelProfilePanel";
 import { useChannelRouteTarget } from "./useChannelRouteTarget";
 import { useChannelOpenReadState } from "./useChannelOpenReadState";
@@ -165,8 +165,8 @@ export function ChannelScreen({
   const mainInsetRef = useMainInsetRef();
   const currentPubkey = currentIdentity?.pubkey;
   const activeChannelId = activeChannel?.id ?? null;
-  const [timelineIsAtBottom, handleTimelineAtBottomChange] =
-    useScopedAtBottom(activeChannelId);
+  const [timelineReadPresence, handleTimelineReadPresenceChange] =
+    useScopedTimelineReadPresence(activeChannelId);
   const isHuddleTranscript = useIsHuddleTranscript(activeChannelId);
   const relaySelfPubkey = useRelaySelfQuery(activeChannel !== null).data;
   const effectiveOpenThreadHeadId = useHuddleThreadIsolation({
@@ -205,23 +205,11 @@ export function ChannelScreen({
   useChannelSubscription(activeChannel);
   const { fetchOlder, hasOlderMessages, historyExhausted, isFetchingOlder } =
     useFetchOlderMessages(activeChannel);
-  const latestActiveMessage = React.useMemo(() => {
-    const messages = messagesQuery.data;
-    if (!messages) return null;
-    for (let index = messages.length - 1; index >= 0; index -= 1) {
-      if (getThreadReference(messages[index].tags).parentId === null)
-        return messages[index];
-    }
-    return null;
-  }, [messagesQuery.data]);
-  const activeReadAt = latestActiveMessage
-    ? new Date(latestActiveMessage.created_at * 1_000).toISOString()
-    : null;
   useChannelOpenReadState(
     activeChannelId,
     activeChannel?.isMember,
-    activeReadAt,
-    timelineIsAtBottom,
+    timelineReadPresence.readAt,
+    timelineReadPresence.isAtBottom,
   );
   React.useEffect(() => {
     if (!activeChannelId) {
@@ -938,7 +926,9 @@ export function ChannelScreen({
                   }
                   onThreadPanelResizeStart={handleThreadPanelResizeStart}
                   onTargetReached={handleTargetReached}
-                  onTimelineAtBottomChange={handleTimelineAtBottomChange}
+                  onTimelineReadPresenceChange={
+                    handleTimelineReadPresenceChange
+                  }
                   onToggleReaction={effectiveToggleReaction}
                   openAgentSessionChannelId={openAgentSessionChannelId}
                   openAgentSessionPubkey={openAgentSessionPubkey}
diff --git a/desktop/src/features/channels/ui/useChannelOpenReadState.ts b/desktop/src/features/channels/ui/useChannelOpenReadState.ts
index 356b28a1e6..d6d61c6f65 100644
--- a/desktop/src/features/channels/ui/useChannelOpenReadState.ts
+++ b/desktop/src/features/channels/ui/useChannelOpenReadState.ts
@@ -22,7 +22,7 @@ export function getTopLevelInboxUnreadOverrideIds(
 export function useChannelOpenReadState(
   activeChannelId: string | null,
   isChannelMember: boolean | undefined,
-  activeReadAt: string | null,
+  activeReadAt: number | null,
   isAtBottom: boolean,
 ) {
   const { feedItemState, locallyUnreadFeedItems, markChannelRead } =
diff --git a/desktop/src/features/channels/ui/useScopedTimelineReadPresence.ts b/desktop/src/features/channels/ui/useScopedTimelineReadPresence.ts
new file mode 100644
index 0000000000..f00a181867
--- /dev/null
+++ b/desktop/src/features/channels/ui/useScopedTimelineReadPresence.ts
@@ -0,0 +1,24 @@
+import * as React from "react";
+
+export type TimelineReadPresence = {
+  isAtBottom: boolean;
+  readAt: number | null;
+};
+
+export function useScopedTimelineReadPresence(
+  scopeId: string | null,
+): [TimelineReadPresence, (presence: TimelineReadPresence) => void] {
+  const [state, setState] = React.useState({
+    isAtBottom: false,
+    readAt: null as number | null,
+    scopeId: null as string | null,
+  });
+  const onPresenceChange = React.useCallback(
+    (presence: TimelineReadPresence) => setState({ ...presence, scopeId }),
+    [scopeId],
+  );
+  return [
+    state.scopeId === scopeId ? state : { isAtBottom: false, readAt: null },
+    onPresenceChange,
+  ];
+}
diff --git a/desktop/src/features/channels/ui/useVisibleChannelReadState.test.mjs b/desktop/src/features/channels/ui/useVisibleChannelReadState.test.mjs
index d8a34a376c..b3ac1437e0 100644
--- a/desktop/src/features/channels/ui/useVisibleChannelReadState.test.mjs
+++ b/desktop/src/features/channels/ui/useVisibleChannelReadState.test.mjs
@@ -41,12 +41,12 @@ test("live channel arrivals advance read state at bottom", async () => {
     isAtBottom: true,
     isMember: true,
     markChannelRead,
-    readAt: "1970-01-01T00:01:40.000Z",
+    readAt: 100,
   };
   const view = await renderReadState(props);
   calls.length = 0;
 
-  view.rerender({ ...props, readAt: "1970-01-01T00:02:00.000Z" });
+  view.rerender({ ...props, readAt: 120 });
 
   assert.deepEqual(calls, [["channel-1", "1970-01-01T00:02:00.000Z"]]);
 });
@@ -59,17 +59,17 @@ test("scrolled-away channel arrivals remain unread until the reader returns to b
     isAtBottom: false,
     isMember: true,
     markChannelRead,
-    readAt: "1970-01-01T00:01:40.000Z",
+    readAt: 100,
   };
   const view = await renderReadState(props);
 
-  view.rerender({ ...props, readAt: "1970-01-01T00:02:00.000Z" });
+  view.rerender({ ...props, readAt: 120 });
   assert.deepEqual(calls, []);
 
   view.rerender({
     ...props,
     isAtBottom: true,
-    readAt: "1970-01-01T00:02:00.000Z",
+    readAt: 120,
   });
   assert.deepEqual(calls, [["channel-1", "1970-01-01T00:02:00.000Z"]]);
 });
diff --git a/desktop/src/features/channels/ui/useVisibleChannelReadState.ts b/desktop/src/features/channels/ui/useVisibleChannelReadState.ts
index 2ce5a71d92..cab557b97e 100644
--- a/desktop/src/features/channels/ui/useVisibleChannelReadState.ts
+++ b/desktop/src/features/channels/ui/useVisibleChannelReadState.ts
@@ -11,10 +11,13 @@ export function useVisibleChannelReadState({
   isAtBottom: boolean;
   isMember: boolean | undefined;
   markChannelRead: (channelId: string, readAt: string | null) => void;
-  readAt: string | null;
+  readAt: number | null;
 }): void {
   React.useEffect(() => {
     if (!channelId || isMember === false || !isAtBottom) return;
-    markChannelRead(channelId, readAt);
+    markChannelRead(
+      channelId,
+      readAt === null ? null : new Date(readAt * 1_000).toISOString(),
+    );
   }, [channelId, isAtBottom, isMember, markChannelRead, readAt]);
 }
diff --git a/desktop/src/features/messages/ui/MessageTimeline.tsx b/desktop/src/features/messages/ui/MessageTimeline.tsx
index 2802d1e11b..c1aee72059 100644
--- a/desktop/src/features/messages/ui/MessageTimeline.tsx
+++ b/desktop/src/features/messages/ui/MessageTimeline.tsx
@@ -23,7 +23,10 @@ import { TimelineSkeleton, useTimelineSkeletonRows } from "./TimelineSkeleton";
 import { TimelineMessageList } from "./TimelineMessageList";
 import type { TimelineVirtualizerApi } from "./TimelineMessageList";
 import { useAnchoredScroll } from "./useAnchoredScroll";
-import { resolveTimelineReadPresence } from "./anchoredScrollPolicy";
+import {
+  resolveTimelineReadPresence,
+  resolveTimelineVisibleReadAt,
+} from "./anchoredScrollPolicy";
 import { useLoadOlderOnScroll } from "./useLoadOlderOnScroll";
 import { useBufferedTimelineMessages } from "./useBufferedTimelineMessages";
 import {
@@ -116,7 +119,10 @@ type MessageTimelineProps = {
   /** The current find-in-channel query string. */
   searchQuery?: string;
   targetMessageId?: string | null;
-  onAtBottomChange?: (atBottom: boolean) => void;
+  onReadPresenceChange?: (presence: {
+    isAtBottom: boolean;
+    readAt: number | null;
+  }) => void;
   onTargetReached?: (messageId: string) => void;
   splitThreadPanelOpen?: boolean;
   /** Event id of the oldest unread top-level message at channel open, or null. */
@@ -206,7 +212,7 @@ const MessageTimelineBase = React.forwardRef<
     searchMatchingMessageIds,
     searchQuery,
     targetMessageId = null,
-    onAtBottomChange,
+    onReadPresenceChange,
     onTargetReached,
     splitThreadPanelOpen = false,
     firstUnreadMessageId = null,
@@ -372,18 +378,22 @@ const MessageTimelineBase = React.forwardRef<
     virtualizerRenderVersion,
   });
 
+  const visibleReadAt = React.useMemo(
+    () => resolveTimelineVisibleReadAt(renderedMessages),
+    [renderedMessages],
+  );
   React.useEffect(() => {
-    // Read presence follows the semantic tail, not the physical virtualizer
-    // floor. While live arrivals are buffered, freezing the rendered tail can
-    // make the shortened DOM report physically at-bottom even though the
-    // reader is still scrolled away from the new messages.
-    onAtBottomChange?.(
-      resolveTimelineReadPresence({
+    // Publish one atomic visibility fact. The loaded query can already contain
+    // buffered arrivals that are absent from renderedMessages, so consumers
+    // must never pair the query's newest timestamp with this timeline's tail.
+    onReadPresenceChange?.({
+      isAtBottom: resolveTimelineReadPresence({
         isPhysicallyAtBottom: isAtBottom,
         isSemanticallyAtBottom,
       }),
-    );
-  }, [isAtBottom, isSemanticallyAtBottom, onAtBottomChange]);
+      readAt: visibleReadAt,
+    });
+  }, [isAtBottom, isSemanticallyAtBottom, onReadPresenceChange, visibleReadAt]);
   const hasConfirmedVirtualizerBottomRef = React.useRef(false);
   const bottomConfirmationChannelRef = React.useRef(channelId);
   if (bottomConfirmationChannelRef.current !== channelId) {
diff --git a/desktop/src/features/messages/ui/anchoredScrollPolicy.ts b/desktop/src/features/messages/ui/anchoredScrollPolicy.ts
index a632ae265a..dc8f6c4a4f 100644
--- a/desktop/src/features/messages/ui/anchoredScrollPolicy.ts
+++ b/desktop/src/features/messages/ui/anchoredScrollPolicy.ts
@@ -42,6 +42,18 @@ export function settleProgrammaticBottomPin(
   );
 }
 
+export function resolveTimelineVisibleReadAt(
+  messages: readonly { createdAt: number; parentId?: string | null }[],
+): number | null {
+  let latest: number | null = null;
+  for (const message of messages) {
+    if (message.parentId != null) continue;
+    latest =
+      latest === null ? message.createdAt : Math.max(latest, message.createdAt);
+  }
+  return latest;
+}
+
 export function resolveTimelineReadPresence({
   isPhysicallyAtBottom: _isPhysicallyAtBottom,
   isSemanticallyAtBottom,
diff --git a/desktop/src/features/messages/ui/useAnchoredScroll.test.mjs b/desktop/src/features/messages/ui/useAnchoredScroll.test.mjs
index 7e04eeb8e3..12f001bf08 100644
--- a/desktop/src/features/messages/ui/useAnchoredScroll.test.mjs
+++ b/desktop/src/features/messages/ui/useAnchoredScroll.test.mjs
@@ -4,6 +4,7 @@ import test from "node:test";
 import {
   getPinnedCenterDrift,
   resolveTimelineReadPresence,
+  resolveTimelineVisibleReadAt,
   settleProgrammaticBottomPin,
   shouldIgnorePinnedCenterScroll,
   shouldSettleForSplitPanel,
@@ -24,6 +25,27 @@ function fakeContainer({ clientHeight, scrollHeight, scrollTop }) {
   };
 }
 
+test("visible read frontier excludes query arrivals buffered outside the rendered timeline", () => {
+  assert.equal(
+    resolveTimelineVisibleReadAt([
+      { createdAt: 100, parentId: null },
+      { createdAt: 110, parentId: "thread-root" },
+    ]),
+    100,
+  );
+
+  const loadedQueryWithBufferedArrival = [
+    { createdAt: 100, parentId: null },
+    { createdAt: 120, parentId: null },
+  ];
+  const renderedTimeline = loadedQueryWithBufferedArrival.slice(0, 1);
+  assert.equal(resolveTimelineVisibleReadAt(renderedTimeline), 100);
+  assert.equal(
+    resolveTimelineVisibleReadAt(loadedQueryWithBufferedArrival),
+    120,
+  );
+});
+
 test("buffered arrivals do not become read when the shortened timeline reports its physical floor", () => {
   assert.equal(
     resolveTimelineReadPresence({